1. Field of the Invention
The present invention relates to a TFT substrate, a liquid crystal display device using same, and a method for manufacturing same.
2. Description of Related Art
TFT array substrates using a thin-film transistor (TFT) as a switching element are widely used in display devices and the like. A technology for obtaining a two-layer structure of a gate line of the TFT array substrate has been disclosed. In Japanese Unexamined Patent Application Publication No. 2002-107762, the gate line has a two-layer structure in which a transparent conductive film and a metal film are successively stacked. The transparent conductive film is identical to the transparent conductive film forming a pixel electrode. Because the gate line terminal has the same configuration as the gate line, the gate line terminal also has a configuration in which a transparent conductive film and a metal film are stacked. In Japanese Unexamined Patent Application Publication No. 2002-107762, a metal film is further stacked on the gate line terminal.
Where the gate line has a two-layer structure as described hereinabove, the uppermost layer of the gate line terminal will be a metal film. This is true when the gate line terminal has a two-layer structure identical to that of the gate line and also when only the gate line terminal has a three-layer structure as described in Japanese Unexamined Patent Application Publication No. 2002-107762. Furthermore, the gate line terminal is also exposed to the outside to enable external connection. As a result, in a case where a metal film of an Al system is used as the metal film, local corrosion occurs on the gate line terminal in an atmosphere in which chlorine or the like is present.
Furthermore, a short ring line is sometimes formed in a TFT array substrate. The short ring line is formed to prevent element abnormalities caused by electric charging when the TFT array substrate is formed. The short ring line is eventually removed by cutting the TFT array substrate. Because the short ring line is formed to stride the cutting line, the short ring line is exposed in the cut surface of the substrate. Since the short ring line extends from a terminal such as a gate line terminal, in most cases the short ring line has a configuration identical to that of the gate line terminal. Thus, the short ring line also has a metal film, and the metal film of the short ring line is exposed in the cut surface. As a result, local corrosion occurs in an atmosphere in which chlorine or the like is present.
In a case of a TFT array substrate for use in a transflective liquid crystal display device, a reflective electrode and a transmissive electrode are used as pixel electrodes. In the step of forming the reflective electrode and transmissive electrode, initially, a transparent conductive film and a reflective film are successively formed. Then, they are sometimes patterned by using a resist having a two-step film thickness. As a result, a photoengraving step can be reduced. However, in patterning using a resist having a two-step film thickness, a film of the reflective electrode is sometimes left due to the effect of step in the terminal region where the transmissive electrode is to be formed. As a result, local corrosion occurs in the same manner as described above. When local corrosion thus occurs, reliability of the TFT substrate decreases.